Maybe need a new Carb and Intake....


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Jul 29, 2019
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Vancouver, B.C, Canada
Okay, so long story short, I have a 1968 Dodge Monaco that's bone stock save for the fact that about 20 years ago, the original 383 2 barrel (stock dual exhaust and 906 heads) was rebuilt with what I assumed was a date correct 4 barrel carter carb and intake manifold. Fast forward to now, the carb has to be rebuilt due to leaking seals. To my surprise, I found that the carb is a Carter 4299s atop a 2205968 intake, which would make them from a 1967 383.
From the research I've done, here's my issue as it stands....
The part numbers for the intake and carb are different from 67' to 68'. Due to the 906 heads, the 68' intake was revised to a medium riser with a 3.44" manifold height and with larger throttle bore sizes that the previous year. The 67' intake was a low riser with a 2.80" manifold height. The 68' intake has a 50% increase in runner CFM volume than the 67' in order to properly compliment the amount of air the 906 heads can move. I'm worried that this intake is starving the engine since it's more restrictive than what the factory originally used. From what I understand even the car's factory 2 barrel intake had these improvements over the 67' intake.
As for the difference between the carbs, the 67 is an AFB while in 68 they used an AVS.
(I honestly don't really know the difference between these two other than the AVS is supposed to be better designed and more efficient- if someone could explain between the two I'd be grateful).
I'm also unsure how large the difference in CFM is between the two. I've found conflicting information that the 4299s flows either 535 or 575 CFM, while in 68' a stock carter 4 barrel would have flowed 600-625 CFM (Having said that, I'm pretty sure that the 4429s is still flowing more air than the factory 2 barrel).
So what I'd like to know is what would you guys do? As far as I see it, an engine is just a big air pump, and the more efficient you can move the air in and out of the engine, the better. The heads and exhaust are fine, but the intake is the weakest link in the chain so to speak. Carb-wise, does anybody know for sure what a carter 4299s 4 barrel flows? If it's 575 CFM then I'll rebuild and keep it, since it's probably still flowing more air than the factory 2 barrel, as well as it's a hell of a lot easier to tune a small carb up than it is a big carb down. Otherwise, I guess my best bet would be to try to find an AVS carb that actually belongs under the hood.
carb tag.jpg
Does it still retain the 2bbl camshaft and single exhaust? If so that is your bottleneck. This carb and intake being small will add low end and off idle responsiveness. I like how they drive. It will have less wide open and high RPM power.

it’s flowing more than a 2 bbl.

Tell us how you drive your car. Do you cruise around like an old man? Do you freeway drive much? How fast do you like to cruise? Do you drag race? Does it ever go wide open? Do you know what rear end gear ratio it has?
The longer runners on the '68 manifold were to improve low end torque coupled with the improved heads. There was a jump on 2BBL engines of 20hp from '67 to '68 as a result of going to the 906 heads with the bigger valves. (From 270 to 290 hp). The main advantage of the AVS carb was that it was slightly larger and had an improved secondary setup. The Air Velocity Secondary, where the carb gets is name, provided for a smoother throttle response at WOT because the air door opened gradually as the air flow increased, this helped eliminate dead spots from over leaning the engine. Was also a much more reliable system than the vacuum diaphragm system used on Holley carbs that often failed to open at all. Changing out the carb and manifold from '67 to '68 units is probably not going to produce a big gain in performance, a little more torque on the low end and a boost in performance if you are running the engine over about 4000 rpms. If you were happy with how it ran before, rebuild the carb and call it good.

Hey guys, thanks for the info. To answer your questions- It seems to run and drive just fine, though it's a little sluggish stoplight to stoplight and more low-end torque would always be nice. It has 2.94 rear gears and will cruise all day on the freeway no problem, regardless if I'm going 55 or 75. I do tend to drive gentle as I'm a little wary of the drum brakes, very few WOT pulls, no drag racing or anything. I'm well aware it's a boulevard cruiser, not a hot rod. The camshaft is stock as far as I'm aware. May replace with with a mild RV or towing spec cam sometime in the distant future. Right now at most, my hope is to make the engine as happy as possible while maximizing my low-end torque. The car+ a full tank of gas+ me+ spare tire and misc fluids/ tools in the trunk = approx 4400-4500 lbs of weight to lug around. Even for a big block 383, that's gotta be a chore.
Simpler swap to maximize the good torque the car already has is to go to a 3:23 gear. You'll definitely notice some oomph off the line, and hardly notice a difference in the top end.
It's one thing to feel that you didn't get what you were supposed to get with the rebuild/upgrade. BUT as long as it works well as is, just repair what you have and be done with it.

As for the stop light grand prix, it's a 4500lb car that takes some torque to move from rest. Sluggish? By what measure. Reason I say that is that I didn't consider our '66 Newport 383 2bbl sluggish as it'd lay rubber from a dead stop, with just "a part-throttle punch" . . . back then. And THAT was with the 2.76 gear. IF you're trying to measure it against something newer with a gazillion-speed automatic (which usually has a 4.5 low gear ratio in the trans, rather than a 2.45), anything will probably be sluggish. Just don't try to race anything with such a modern trans as you'll probably get embarrassed. One reason is the powertrain gearing, another reason is their lighter weight.

Heavier cars with "highway gears" don't normally respond well to WOT right off of idle, from my experiences. Part-throttle punch which leads to WOT works better.

Manually shifting 1-2 might help, but not the off-idle response.

For best results, pay attention to how the car works best and enjoy what it DOES do.

Thoughts and observations,
IDK my 68 2bbl 383 2.76:1 seems to do fine with stop light traffic when they don't notice that you're going to zoom away. Then again my car is much happier on the highway
Okay, I had an old mechanic buddy of my dad's take a quick look at the car since he's going to be the one rebuilding the carb. Turns out the carb is in a lot worse shape than I thought. The primary's open but not all the way, and the secondary are more or less seized, so it's been running as a 2 barrel this entire time I've had it. Second is that the shift linkage between the carb and the transmission is a jerry-rigged mix of linkage parts and the transmission as such isn't getting power to the wheels as good as it should be. He took it for a short drive, said that from a dead stop, it almost felt like sometimes it was starting in second, but it would shift into 1st if you slowed down from speed. We also checked the plugs, looks like the engine's been running a little lean, but only a bit. He told me he was amazed it ran/ drove as well as it did considering the issues we uncovered, and the sluggishness I'm feeling around town is more likely than not related to these issues. I've already ordered a Bouchillion Performance kickdown linkage kit to solve the linkage issue, and the carb rebuild should should fix everything else. He might actually have an edelbrock performer intake manifold for a 383 as well- an old customer of his was restoring a New Yorker and it was swapped out for a factory manifold, there's a chance it may be laying somewhere around the shop still. Apparently there's less than 1500 km's/ 950 miles on it and he'll throw it on for a case of his favorite beer and if I supply the gaskets, so we'll see if he can find it or not.
Otherwise, thanks for all the help guys! This is my first C-body and from looking at the posts, it looks like they drive a hell of a lot better than what I'm experiencing at the moment. All this work will be getting done in the next month or so, but I'll keep things updated as they happen!